The present invention relates to an electric contact material useful in the fabrication of a relay for use in vehicles, the relay being highly durable against load exerted by a magnetic clutch of a vehicle air-conditioner. The invention also relates to such a relay for use in vehicles.
An electric contact element which makes and breaks an electric circuit is generally called an electric contact. The electric contact must allow current (signal) flow via the contact through contact between metal parts. In addition, the electric contact must completely break the circuit upon breaking of contact.
Although an electric contact per se has a simple structure, a variety of physical and chemical phenomena are known to occur at a contact surface thereof. For example, there occur adsorption, oxidation, sulfidation, and formation of organic compounds, and concomitant discharge, melting, evaporation, wear, and transfer. Such phenomena are very complex, and as a result, the phenomena have not yet been completely elucidated in studies thereon.
The occurrence of such phenomena adversely affects the function of the electric contact, in some cases leading to inhibition of the contact function (for example, the contact portions become welded together). Loss of the contact function is detrimental to the performance and service life of the electrical appliance into which such an affected electric contact is incorporated. Therefore, an electric contact is one of the important parts for determining the service life and performance of an electrical appliance.
In recent years, remarkable developments in the field of electronics and electrical engineering have made a broad range of appliances employing electric contacts available; i.e., from light electrical appliances such as apparatuses for telecommunications and electronics to heavy electrical appliances such as large-current choppers. Since the functions required vary depending on use, electric contacts having characteristics suited to various end uses have been developed. In fact, a large variety of such apparatuses are commercially available.
The existing techniques related to the types of electric contacts according to the present invention; i.e., those contacts used in relays and switches for use in vehicles, will next be described. An electric contact element which is to be used in relays and switches is called a make-and-break contact. The electric contact material for producing such a make-and-break contact is particularly required to have wear resistance and transfer resistance in order to maintain a stable make-and-break mechanism, and to have low contact resistance in order to maintain stable contact conditions.
Examples of electric contact materials conventionally employed for fabricating relays and switches for use in vehicles include Agxe2x80x94Cu alloys (1-25 wt. % Cu, the balance being Ag), Agxe2x80x94SnO2 alloys (5-15 wt. % SnO2, the balance being Ag), and Agxe2x80x94SnO2xe2x80x94In2O3 alloys.
These electric contact materials may be used by themselves in unmodified form. However, usually, these materials are formed into a clad rivet contact in which two to three contact layers are laminated on a Cu or Cu alloy layer serving as a substrate layer or into a clad crossbar contact in which two to five contact layers are laminated on a Cu or Cu alloy layer serving as a substrate layer. The clad rivet contact and the clad crossbar contact are useful in the fabrication of a relay, in which an electric contact can make and break electric contact by the action of a movable iron plate which is brought into contact to a counterpart through a magnetic force produced by applying an electric current (signal) such as direct current, alternating current, or impulses to a coil in order to generate magnetic flux.
When exposed to direct-current loads in vehicles, the aforementioned conventional electric contact materials are satisfactory at a practical level in terms of wear resistance, transfer resistance, and low contact resistance. However, the following problems have been identified. Firstly, these electric contact materials do not meet demand for the smaller-sized parts of vehicles. As the functionality and performance of vehicles has increased, the number of electric parts used in vehicles has also increased, but the size of the electric parts themselves has decreased. In addition, size reduction has been performed also in consideration of cost reduction. Although there is demand for size reduction of relays and switches themselves, the aforementioned conventional electric contact materials do not lend themselves to this purpose.
Briefly, when the volume of an electric contact material decreases so as to reduce the size of a relay, the work per unit volume of the material increases greatly during the making and breaking of contact. Thus, a conventional electric contact material undergoes self-welding only after a short period of operation.
Secondly, in recent years, in addition to size reduction, there is also demand for extending the range of applications and for extending the service life of relays and switches for use in vehicles. Regarding extending the range of applications, there is demand for electric contact materials which can generally be suited for operation of a variety of loads; e.g., lamp loads where there is a flow of inrush current (head lamps and discharge lamps), resistance loads (rear defogger), and solenoid loads in which long-term arc generation occurs (magnetic clutch).
Regarding the extension of service life, there are needed electric contact materials which can be operated for a long period of time even when the electric appliance is used in a novel operational mode. For example, operation of a vehicle air-conditioner has undergone various changes. Previously, vehicle air-conditioners were usually operated only in summer. However, recently, air-conditioners have been operated throughout the year as automatically-controllable air-conditioners. Consequently, operational frequency and the operation period of relays and switches to control the air-conditioners has increased correspondingly. Thus, there is a requirement for electric contact material useful in the fabrication of make-and-break contacts to satisfy the above conditions.
Examples of relays which are currently and typically used in vehicles include an ISO (International Standardization organization) relay, a mini-ISO relay, and a micro-ISO relay. By employing Ag material such as Agxe2x80x94SnO2 or Agxe2x80x94SnO2xe2x80x94In2O3 to fabricate such relays, a considerable reduction in size has already been attained. However, currently employed relays used to control a magnetic clutch of a vehicle air-conditioner are not sufficiently durable. At present, simultaneous extension of both the applications and the service life of the above relays has not yet been attained.
Specifically, an open-type relay is employed as a vehicle relay for controlling a magnetic clutch which exerts an inductive load (50W) on a vehicle air-conditioner. Currently, an open-type relay has attained a durability equal to approximately 400,000 cycles of make-and-break operation. Thus, there is a further need for a relay, for use in vehicles, having a durability equal to at least 1,000,000 cycles of make-and-break operation so as to suit the relay for the aforementioned increased frequency of make-and-break operations.
The present invention has been accomplished in consideration of the foregoing. Accordingly, the invention is directed to an electric contact material useful in the fabrication of a vehicle relay of high durability against inductive load to which the relay incorporated in a magnetic clutch of a vehicle air-conditioner is exposed, and also to a relay having remarkable durability as has never been attained for use in vehicles.
In order to solve the aforementioned problems, the present inventors have conducted extensive studies and experiments on the composition of electric contact material for controlling a magnetic clutch (i.e., an inductive load) of a vehicle air-conditioner and the circumstances under which the contact material is used, and have developed a relay for use in vehicles as described below.
Accordingly, as described in claim 1, there is provided an electric contact material useful in the fabrication of a relay for use in a vehicle, the relay controlling a magnetic clutch (i.e., a load) of a vehicle air-conditioner, wherein the material comprises an Agxe2x80x94SnO2xe2x80x94In2O3 alloy which is produced through internal oxidation of an Agxe2x80x94Snxe2x80x94In alloy containing 5.0-10.0 wt. % (as reduced to metal) Sn and 2.0-5.0 wt. % In, the balance being Ag, and is used in a shielded space.
As recited in claim 2, there is provided an electric contact material useful in the fabrication of a relay for use in a vehicle, the relay controlling a magnetic clutch (i.e., a load) of a vehicle air-conditioner, wherein the material comprises an Agxe2x80x94SnO2xe2x80x94In2O3xe2x80x94NiO alloy which is produced through internal oxidation of an Agxe2x80x94Snxe2x80x94Inxe2x80x94Ni alloy containing 5.0-10.0 wt. % (as reduced to metal) Sn, 2.0-5.0 wt. % In, and 0.01-0.50 wt. % Ni, the balance being Ag, and is used in a shielded space.
The electric contact materials according to the present invention useful in the fabrication of a relay for use in a vehicle, the relay controlling a magnetic clutch (i.e., a load) of a vehicle air-conditioner, have remarkably increased the durability during operation of a magnetic clutch (i.e., an inductive load) of a vehicle air-conditioner. In addition, the electric contact materials exhibit durability equal to that which has conventionally been attained during the operation of other loads in vehicles, such as vehicle lamps. Thus, the material sufficiently is suited to long-term operation and application in a small device.
In general, electric contact material useful in the fabrication of a relay for use in vehicles, such as a micro-ISO relay, is used while the material is in contact with airs i.e., is used in an open system. However, the present inventors have investigated the composition of electric contact material useful in the fabrication of a relay for use in vehicles such as a micro-ISO relay and the circumstance under which the material is used, and have found that the electric contact material as recited in claim 1 or 2 in a shielded space attains a durability at least twice that of the conventional electric contact material useful in the fabrication of a relay for use in vehicles, the relay controlling a magnetic clutch (i.e., load) of a vehicle air-conditioner.
The present inventors have recognized the reason why the electric contact material useful in the fabrication of a relay for use in vehicles has remarkably increased durability. Briefly, the durability of electric contact material for operation of a magnetic clutch (i.e., inductive clutch) of a vehicle air-conditioner is determined by the type of wear to which the contact material is subjected.
In general, there are two types of wear of electric contact material for use in vehicles employing a power source (DC 14 V); (1) the case in which a positive electrode material is worn by a metal phase arc, thereby dispersing the formed powder around the contact material and (2) the case in which a negative electrode material is worn by a metal phase arc and a subsequently generated gas phase arc, thereby dispersing the formed powder around the contact material and transferring a material from the negative electrode to a positive electrode.
In practical applications, the type of wear of electric contact material for operating lamps (i.e., loads) such as head lamps and resistance (i.e., a load) (rear defogger i.e., resistance heating wire for defogging a rear window of a vehicle) is known to be categorized as case (1), whereas the type of wear of electric contact material for operating inductive loads such as a magnetic clutch of a vehicle air-conditioner is known to be categorized as case (2).
The present inventors have conducted studies on Agxe2x80x94 containing electric contact material useful in the fabrication of a relay for use in vehicles for operation of elements (i.e., loads) where the type of wear associated with case (2) manifests itself, and have found that when the material is used in an open system, arcs are focused on a certain portion of the electric contact, thereby forming projections and craters on a contact surface during an initial stage of make-and-break operation. Once such projections and craters have been formed, arcs are further focused on the projections, thereby accelerating the growth of projections and craters. The growth of projections and craters reduces the contact gap (minimum distance between contact parts), thereby prolonging the period during which the arc continues. This in turn further promotes the formation of projections and craters, thereby accelerating the deterioration of the electric contact. Finally, the contact attains a locking state (projections and craters are mechanically locked together) which causes malfunctions in the apparatus containing such an electric contact or readily causes self-welding thereof. Since these projections are formed through transfer of a material from a negative electrode to a positive electrode, the projections have an oxide-poor (loss of oxide) metallographic structure as compared with the initial state of the contact material. The welding resistance of such electric contact materials depends on the amount of oxide contained in the materials. Thus, projections containing a lesser amount of oxide exhibit low welding resistance, thereby readily undergoing self-welding.
On the basis of the results of the above research, the present inventors have investigated the composition electric contact material and the circumstance under which the materials are used, and have proposed the use of the electric contact material as recited in claim 1 or 2 in a shielded space so as to inhibit formation of projections and craters during an initial stage of make-and-break operation. The inventors have further elucidated that the durability can be enhanced stably by filling the shielded space with a gas other than an oxygen-containing gas such as air; i.e., with an oxygen-free gas. Also, the inventors have confirmed that is a preferred oxygen-free gas in actual practice argon or nitrogen.
The reason why the electric contact material according to the present invention useful in the fabrication of a relay for use in vehicles can prevent formation of projections and craters during an initial stage of make-and-break operation is considered to be due to the following mechanism.
In general, when an Agxe2x80x94 containing electric contact material is used in an open-type relay for use in vehicles, a metal phase arc is generated at a contact surface by breaking the contact, and a subsequently generated gas phase arc forms a molten portion in Ag. Since the solubility limit of oxygen in molten Ag is 0.32 wt. % (960.5xc2x0 C.), molten Ag immediately takes in oxygen to form a solid solution. Subsequently, molten Ag begins to solidify through heat diffusion while in contact with a non-molten portion. Since the solubility limit of oxygen in Ag solid is considerably low (0.01 wt. % at 939xc2x0 C.) as compared with the case of molten Ag), a certain amount of oxygen which cannot be dissolved is released from Ag solid in the form of oxygen gas. In this case, Ag solidifies into foam-like Ag solid containing bubbles. Then, when the relay operates, another arc is generated at a portion where the Ag solid has acquired this foam-like form. Subsequently, foamed Ag is then transferred from a negative electrode to a positive electrode through the action of a gas phase arc and is deposited on the surface of the positive electrode. Repetition of the process results in the formation of projections and craters on a contact portion.
However, since the electric contact material according to the present invention useful in the fabrication of a relay for use in vehicles is used in a shielded space, the aforementioned foaming of Ag and concentration of arcs are prevented, thereby inhibiting formation of projections and craters. Thus, the durability of the electric contact material can be remarkably enhanced.
The electric contact material according to the present invention useful in the fabrication of a relay for use in vehicles comprises an Ag-base material. The effects of incorporation of other component elements; i.e., Sn, In, and Ni, and the reason why the amount of each element has been determined will be described hereunder.
The element Sn is contained in the electric contact material in the form of SnO2. Sn contributes to enhancement of welding resistance of the electric contact material for operation of loads, such as a lamp load, in which there is a flow of inrush current. The amount of Sn is limited to 5.0-10.0 wt. % for the following reasons. Briefly, when the amount is less than 5.0%, the electric contact material useful in the fabrication of a relay for use in vehicles cannot maintain an acceptable level of welding resistance. Particularly, this tendency is more clear in the case of operation of a lamp (i.e., a load). When the amount is in excess of 10.0 wt. %, processability of the contact material decreases, thereby affecting the production of electric contacts. When the electric contact material is employed in a shielded space for operating a magnetic clutch (i.e., a load) of a vehicle air-conditioner, an amount of Sn of 6.5-9.0 wt. % is particularly preferred, in view of electric contact characteristics.
The element In is contained in the electric contact material in the form of In2O3. The In contributes to enhancing wear resistance of the electric contact material used to operate a magnetic clutch (i.e., an inductive load) of a vehicle air-conditioner. The amount of In is limited to 2.0-5.0 wt. % for the following reasons. Briefly, when the amount is less than 2.0 wt. %, the electric contact material has poor wear resistance during operation of a magnetic clutch (i.e., an inductive load) of a vehicle air-conditioner, thereby failing to attain an acceptable level of durability. When the amount is in excess of 5.0 wt. %, the high cost of In disadvantageously elevates the product price. When the electric contact material is employed in a shielded space for operating a magnetic clutch (i.e., a load) of a vehicle air-conditioner, an amount of In of 3.6-4.5 wt. % is particularly preferred, in view of electric contact characteristics.
Ni serves as an element for depositing oxide micrograms in Ag during internal oxidation to form Agxe2x80x94SnO2xe2x80x94In2O3 alloys and enhances welding resistance and wear resistance of electric contact material. The amount of Ni is limited to 0.01-0.50 wt. % for the following reasons. Briefly, when the amount is less than 0.01 wt. %, the effect of depositing oxide micrograms cannot be attained, whereas when the amount is in excess of 0.50 wt. %, Ag and Ni assume two separate phases in a molten state, thereby causing segregation of Ni during casting, possibly leading to a problem in product quality. When the electric contact material is employed in a shielded space for operating a magnetic clutch (i.e., a load) of a vehicle air-conditioner, an amount of Ni of 0.05-0.20 wt. % is particularly preferred, in view of electric contact characteristics.
Needless to say, use of the electric contact material according to the present invention in a shielded space attains a durability at least twice that of conventional electric contact material useful in the fabrication of a relay for use in vehicles, the relay controlling a magnetic clutch (i.e., a load) of a vehicle air-conditioner.